Phase transformer arrangements and induction machines employing phase transformer arrangements



7 Sheets-Sheet 1 PRIMARY SECDMMR Y f PHMARY INVINTORS FREDERIC cALLA uAMS :ma Rosiers Lam-l MT5. Jouw Fkenemck EASTHAM BY SiuwmMAhM'KMl-N ATTORNEYS PHASE TRANSFORMER ARRANGEMENTS AND INDUCTION MACHINES June 19, 1962 Filed Oct. 5, 1959 F. C. WILLIAMS ETAL `lune 19, 1962 3,040,226

PHASE TRANSFORMER ARRANGEMENTS AND INDUCTION MACHINES EMPLOYING PHASE TRANSFORMER ARRANGEMENTS '7 Sheets-Sheet 2 Filed Oct. 5, 1959 dag INVENTORS FREDERlc CALLAND WILLIAMS ERIC teasers LAITHWMTE JOHN FREDEMCK EASTHAM BY S'm, nmlmm'kqa a ATTORNEY 5 `lune 19, 1962 F. C, W|L |AMS ETAL 3,040,226

PHASE TRANSFORMER ARRANGEMENTS AND INDUCTION MACHINES EMPLOYING PHASE TRNSF'ORMER ARRANGEMENTS Filed 001;. 5, 1959 7 Sheets-Sheet 5 INVENTORS FZRDERIC CALL/.No WILLIAMQ Elle KoBEQTS L AITHWAIT: Jam Fnsnemcz eAsTHAM ATTORNEY June 19, 1962 F. c. WILLIAMS l-:TAL 3,040,226

PHASE rrRANsEoRMER ARRANGEMENTS AND INDUCTION MACHINES EMPLoYING PHASE TRANsEoRMER ARRANGEMENTS Filed Oct. 5, 1959 '7 Sheets-Sheet 4 PS3 PS4 PS5 PS6 INVENTORS Feoazlc CALI-AND wLuAMS smc Rasmus LAlrHwAA-rs Jean Fzsoselcu EASTHAM.

I BY Sim, gmmwknm ATTORNEY 5 June 19, 1962 F. c. WILLIAMS ETAL 3,040,226

PHASE TRANSFORMER ARRANGEMENTS AND INDUCTION MACHINES EMPLOYING PHASE TRANSFORMER ARRANGEMENTS 7 Sheets-Sheet 5 Filed Oct. 5 1959 June 19, 1962 F. c. WILLIAMS ETAL 3,040,226

PHASE TRANSFORMER ARRANGEMENTS AND INDUCTION MACHINES EMPLOYING PHASE TRANSFORMER ARRANGEMENTS Filed OCI. 5, 1959 'I sheets-sheet e l l l l INVENTORS AMS ATTORNEYS I-IzI-z n w25 wmke JOHN FREDERICK EASTHAM BY s......,m. MIwnhnmmf 3 3 3 w I- 55-1-.. 1./ 6 2 6 3 x/ 6 3/../ 6 3 fr, 6 3. 6 w37. ,.6 Il 6 I /rMM M 6 6 1 )f 6 2 6 3 6 ou) f5 3 ry. 6 3). rrr/6 e ln/ 9 2 f/ r6 2 2 f al f. 6 3) /z/ f/ 6 3.2./ f 6 3 /1 6 ||I ./IIIIIIIBIIIIl 3 J. 3 3

June 19, 1962 F. c. WILLIAMS ETAI. 3,040,226

PHAsE rrRANsEoRMER ARRANGEMENTS AND INDUCTION MACHINES EMPLOYING PHASE TRANsFoRMER ARRANGEMENTS Filed oct. 5 1959 7 sheets-sheet 7 NVENTORS FREDERIC cALLANn II.I.IAMS

ERIC ROBERTS LAITHWAITE JoI-IN FREDERICK EASTHAM United States Patent 3,040,226 PHASE TRANSFRMLER ARRANGEMENTS AND INDUCTION MACHINES EMPLQYING PHASE TRANSFQRMER ARRANGEMENTS Frederic Caiiand Wiiliams, Romiy, Eric Roberts Laith- Waite, Manchester, and John Frederick Eastham, Preston, Engiand, assignors to National Research Development Corporation, London, England, a British corporation Filed 9ct. 5, 1959, Ser. No. 844,457 7 Claims. (Cl. S18- 205) The present invention relates to induction machines and is more particularly concerned with polyph-ase induction machines of variable speed where the variation in speed is controlled by varying the phase of the currents supplied to the machine. The invention is also concerned with phase-shifting devices for use with polyphase currents which is capable of use for varying the phase of the currents supplied to the induction machine.

`In known types of polyphase induction machines, the primary winding consists of groups of conductors arrangedin slots in such a manner that the phase diierence between the total effective currents flowing in the conductors of adjacent slots is the same as that between the total effective currents flowing in the conductors of any other adjacent slots. It is this phase difference and the spacing of the slots which determines the speed of the motor. Hence any variation in the phase diier'ence or in the spacing of the slots will enable variation in the speed of the motor to be obtained. Examples of motors where the speed variation was obtained by eiiectively altering the spacing of the slots are contained in United States Patent 2,856,573 and United States application 582,829, abandoned in favor of application Ser. No. 851,773, led November 9, 1959, now Patent No. 2,978,623. The object of the present invention is to provide an improved primary winding for an induction machine which enables the speed of the machine to be varied by varying the phase difference between the total effective currents ilowing in the conductors of adjacent slots.

A further object of the invention is to provide a phase shifting device which is fed from a polyphase supply and which has a plurality of outlets, the phase difference between the currents flowing in adjacent outlets being the same and capable of variation.

According to the invention, in a polyphase inductionA machine having a discontinuous primary winding consisting of at least two sets of coils provided in slots substantially transverse to the direction of movement of a secondary winding, the magnetomotive force in at least some of the slots is generated by the addition of the magnetomotive forces caused by current -flow in the conductors of coils of two sets and each set of coils is so arranged that`the magnitude of the current flow in the conductors of a slot carrying .coils of the same phase is different for the diterent slots while current is fed to the sets of coils in such a manner that the phase difference between the current flow in the conductors off coils of two sets in each slot carrying conductors of two sets of coils is the same for all slots, means being provided for varying the phase difference in order to vary the speed of movement of the secondary winding.

According to ean aspect of the invention, in a polyphase induction machine having a discontinuous primary winding consisting of at least two sets of coils provided in slots transverse to the direction of movement of a secondary Winding, the magnetomotive force in at least some of the slots is generated by the addition of the magnetomotive -forces caused by current iiow in coils of two sets and each set of coils is so arranged that the magnitude of the current flow in the conductors ot a slot carrying coils 3,040,226 Patented June 19, 1962 of the same phase is different for the diiferent slots while current is `fed to the coils of the Ilrst set directly from the mains supply `and to the coils of a second set from a phase-shifting arrangement to which current is fed from the mains supply whereby the phase difference between the current flow in the conductors of coils of two sets in each slot carrying conductors of the two sets of coils is the same for Aall slots and is capable of variation by `adjustment of the Vphase-shifting arrangement, in order to vary the speed of movement of the secondary winding.

According to another aspect of the invention, in a polyphase induction machine having a discontinuous primary winding consisting of a plurality of sets of coils provided in slots transverse to` the direction of movement of a secondary winding, the magnetomotive force in at least some of the slots is generated by the addition of the magnetomotive forces caused by current iiow in the conductors of two sets of coils and each set of coils is so arranged that the magnitude of the current flow in the conductors of a slot carrying coils of the same phase is diiterent for different slots while current is `fed to the coils of a rst set directly from the mains supply and to the coils of a second and third set from a iirst and a second phaseshifting device respectively which introduce equal and opposite phase ditr'erences with respect to the mains supply, the second set of coils overlapping the one end of the iirst set of coils while the third set of coils overlaps the other end whereby the phase dilerence between the current flow in the conductors of coils of two sets in each slot carrying conductors of two sets of coils is the same for all slots and is capable of variation by `adjustment of the phase-shifting devices in order to vary the speed of movement of the secondary winding.

According to a further aspect of the invention, a phaseshifting device for use with polyphase currents comprises `a transformer arrangement having for each phase a primary winding formed by a plurality of coil assemblies 'y equal in number to the number of outlets required and fed from one phase of the polyphas'e supply, the number of poles generated by successive coil `assemblies being in the ratio 1:11 where n is an integer greater than l, and a secondary winding formed by a plurality of coil assemblies having the same configuration as those of the primary winding and individually connected to different outlets, means being provided for effecting relative movement between the structure carrying the primary winding and the structure carrying the secondary winding whereby the phase angle between the current in each of the phases fed to the primary winding and the current in the corresponding outlets of the secondary winding is given by 6 and 20, 36' or n0 where 0 is dependent on the degree of relative movement between said two structures.

It should be mentioned that the terms primary winding and secondary iwinding have been used in place of the more usual terms stator winding and rotor lwinding respectively. It is considered that the terms used herein are more satisfactory in View of the fact that rotor is an ambiguous term where referring to a linear machine to which the present invention could be applied. Further the terms used herein are in accordance with theoretical considerations if the induction machine is regarded as a transformer.

lt will also be understood that while the secondary winding is usually considered as the moving part of the machine, this need not always be so and in some applications of the invention the secondary winding is xed and the primary winding moves.

The invention will be better understood from the following description taken in conjunction with FIGS. l to 17 of the accompanying drawings. In the drawings:

FIG. 1 shows diagrammatically the coil assemblies for the primary and secondary windings of the phase-Shifting device for the case where n; 2,

FIG. 2 shows diagrammatically the coil assemblies for the primary and secondary windings for the case where n=4,

FIG. 3' shows a diagrammatic representation of a constructional form of the phase-shifting device,

FIGS. 4 and 5 are vector diagrams for use in explaining the operation of the induction machine,

FIGS. 6 to 9 show diagrammatically the connections between the phase-shifting device or devices and the induction machine for different embodiments of the invention,

FIGS. l to 14 show'winding plans for the primary winding of dilerent embodiments of the invention,

FIGS. and 16 which should be arranged side-byside along the line A-B show an alternative winding plan to that of FIG. 13 and FIG'. 17 shows diagrammatically a constructional form of an induction machine according to the invention.

Referring first to the principles of operation of the induction machine, consider a primary winding in which the conductors in the slots derive their current partly from the mains supply and partly from a phase-shifting device, the currents in the conductors being such that the sum of the magnetomotive forces generated by the currents is equal in all slots in the case where the phaseshifting device is adjusted to introduce Zero phase change i.e. 0:0. Such a condition is represented by the vector diagram of FIG. 4 for 12 slots. Thus as regards slot 1, the vector OA represents the magnetomotive force due to the current from the mains supply while the vector AB represents the magnetomotive force due to the current from the phase-shifting device. Since 0:0, the addition of these two vectors gives the straight line resultant DAB, and similarly for the magnetomotive forces in the remaining slots. The result is therefore a conventional primary winding for an induction machine.

Now assume that the phase-shifting device introduces a phase change of 0 with respect to the mains supply. The vector OA will not change but the vector AB will now be at an angle 0 to the vector AB and the sum of the magnetornotive forces will be obtained by the usual method of vector addition. FIG. 5 illustrates the case where 0:90 degrees, and shows the vector AB at right angles Vto the vector OA giving the resultant OB i.e. OB is thesum of the magnetomotive forces in the first slot. The sum of the magnetomotive forces in the second slot is shown by the vector O2 and so on for the remaining slots. It will be seen from this drawing that the phase of the magnetomotive forces is progressively advanced from slot to slot compared with the magnetomotive force due to the mains current alone and the phase advance in the 12th slot amounts to 90 degrees. It will, of course, be understood'that if the phase-shifting device introduces a phase change in the opposite direction to that shown in the drawing, the phase of the magnetomotive forces is progressively retarded from slot to slot. Therefore, the introduction of a phase change by the phaseshifting device progressively changes the phase angle between the magnetomotive forces in adjacent slots so that 'a change occurs in the velocity of movement of the moving magnetic iield. Effectively, the operation may be regarded as one of pole stretching" and pole shrinking, giving rise to a varying pole pitch and hence a varying speed.

A variable speed induction machine according to the invention will therefore have a primary winding which does not eXtend around the whole of the secondary winding and will be provided with slots which are substantially transverse to the direction of movement of the secondary winding. The primary winding will, in the simplest embodiment of the invention, consist of two sets 4 of coils, one of which is energised by current from the mains while the other is energised by current obtained from a phase-shifting device. This embodiment is shown in block schematic form in FIG. 6, which shows the eX- lternal connections for one phase between the phase-shifting device PS and the machine MA, and in FIG. 12 which shows the winding plan of the primary winding. Referring to FIG. 6, a mains supply M'is connected in series to terminals 1 and 2 of the phase-shifting device PS and the machine MA. The output from the phase-shifting device is taken from terminals 3 and 4 and fed to correspondingly numbered 4terminals of the machine MA. In FIG. 12, the two sets of coils forming the primary winding are shown, the set M being fed directly from the mains while the set 0, which overlaps the set M, is

fed from the phase-shifting device. The numerals at the top of each set of coils indicate the number of turns in the coils while those below the coils indicate the total number of conductors per slot, the slots being assumed to run vertically. Further the phase of the coils are distinguished by the use of a hrm line for the blue phase, a dotted line for the yellow phase and a dot-dash line for the red phase and the usual sequence R, -B, Y, R, B, -Y is employed. The effective portion of the primary winding is that between the two vertical dotted lines and it desired the threecoils on the left of the mains fed set M and the three coils on the right of the set 0 fed from the phase-shifting device may be ring Wound. Considering FIG. l2 in more detail, it will be seen that the right-hand slot of the mains fed winding M carries a coil of one turn fed with current of the yellow phase. The fourth slot from the right also carries a coil of one turn fed with current of the yellow phase and in addition a coil of 3 turns fed with current of the yellow phase. The current in the conductors of the slots fed from the same phase of the supply is -thus different for different slots. The same also applies to the winding fed from the phase-shifting device. Further since, with the exception of the left-hand slot, each slot contains coils of each set, a variation in 0 causes a variation in the phase difference between the current flow in the conductors of the coils of the two sets of each slot. However, values of 0 greater-than 90 degrees are not very satisfactory due to the fact that the magnetomotive forces are added vectorially and the resultants for 0 greater than degrees are therefore much smaller than the arithmetic sum. The speed range of the machine shown in FIG. l2 is thus limited.

The speed range rnay be increased, however, by providing an additional set of coils fed from a second phaseshifting device. The winding plan for the mains fed set of coils for this embodiment and a further embodiment is shown in FIG. 10 for one slot per pole per phase while the winding plan for two slots per pole per phase is shown in FIG. l1, the numerals having the same signicance as in FIG. 12. Since the magnetomotive force generated by the coils is dependent on the current low through the coils and also on the number of turns in each coil, it will be seen that the magnetomotive force generated by current flow in the conductors `of a slot is different for different slots in the arrangements shown in FIGS. 10 and ll. The winding plan for the complete primary winding is shown in FIG. 13 while the block diagram is shown in FIG. 7. Referring to FIG. 7, the two phase-shifting devices PS1 and PS2 are arranged to.

introduce equal and opposite phase shifts with respect -to the mains, the output from the phase-shifting device PS1 ybeing taken from terminals 3` and 4 and vapplied to one set of coils of the machine MA over terminals 1 and 2. Similarly the output `from the other phase-shifting device PS2 is taken from terminals 3 and 4 and applied to another set of coils of the machine MA over terminals V5 and 6. The mains supply M is fed to the two phase-shifting devices and the mains Ifed set of coils acarrear;

is shown in FIG. 13 and here again it will be seen that `for each set of coils the current in the conductors of the slots fed from the samev phase is different for different slots. However, in this case since positive and negative values of are available respectively from the 0 set of coils fed by one phase-shifting device and 'from the -6 set of coils fed by the other phase-shifting device, the maximum phase change, which is introduced when 9:90 degrees, will be 180 degrees. Thus if the machine is constructed to operate as a 6-pole machine with 6:0, it will operate as a S-pole machine for 0:-90 degrees and as a 7-pole machine for 0=|9O degrees, thereby ygiving a speed ratio of approximately 1.4 to 1 with all intermediate values.

Y The speed range of the machine can be extended by the addition to the primary winding of further sets of coils and additional phase-shifting devices. Thus as shown in FIG. 14 one further set of coils `-l-Z@ overlap the set of coils |0 and another set of coils -20 overlap the set of coils 0, the set of coils 26 being fed from a phase-shifting device which introduces a phase shift of 20 when the phase-shifting device feeding the 0 coils introduces a phase shift of 9, and similarly for the set of coils 20. Theoretically this process may be continued indefinitely but there is obviously a limit to the size of the machine which limits the number of sets of coils which can be accommodated. In addition, the economic factor is also important in determining how far the process should be carried. The connections Abetween the four phase-shifting devices PS3 to PS6 and the machine MA having a primary winding according to FIG. 14 are shown in FIG. 8 which -it is believed will be readily understood from the ydescription already -given of FIGS. 6 and 7.

An economy can be introduced into the arrangement shown in FIG. 8 by combining the phase-shifting devices PS3, PS4 and PS5, PS6 into two phase-shifting devices each having two outlets, the phase shift introduced into one outlet being twice that introduced by the other. Such an arrangement is shown in FIG. 9 where the two phaseshifting devices are indicated by PS7 and PS8. The two outlets of the phase-shifting `device PS7 are taken from terminals, 4 and 5, 6 and the phase difference with respect to the mains introduced in the outlet taken from terminals 3 and 4 is 0 while that introduced in the outlet taken from terminals and f6 is 26. The outlet from terminals 3 and 4 will be connected through terminals 3 and 4 of the machine to the `-lset of coils shown in FIG. 14 while the outlet from terminals 5 and 6 will be connected through terminals 1 and Z of the machine to the set of coils shown in FIG. 14. The outlets -0 and -20 from the phase-shifting `device PS8 will be similarly connected to the-0 and -29 sets of coils shown in FIG. 14. A phase-shifting device capable of introducing integrally related phase shifts into different outlets will be described subsequently.

An alternative winding plan to that of FIG. 14 is shown in FIGS. 16 and 17 where the slots in the structure carrying the primary winding are shown. The coils in the upper portion of the slots are fed from the phasevrshifting devices while those in the lower portion of the slots are fed from the mains, the letters indicating the phase of the current fed to the coils and the numerals the number of conductors in the slots.

It will be understood that the constructional form of the induction machine according to the invention will not differ greatly in appearance from known types of induction machines except for the discontinuous primary winding. A constructional lform of the machine is shown in FIG. 17 with the coils of the primary winding omitted in order to simplify the drawing. Referring to IFIG. 17, the structure 20 carrying the primary winding is cylindrical in shape -and is mounted on a base 21. Sheet iron laminations 22 of arcuate shape having an angle of, for example, 240 `degrees are secured to the inside of the structure 20, the laminations being provided with slots 23 6? to accommodate the primary winding. The structure 24 carrying the secondary winding is also cylindrical and is mounted on a shaft 25 carried in .bearings 26 secured to the base 21. The secondary winding is of the cage type, the structure 24 consisting of sheet iron laminations provided with slots containing the copper bars 27 which form the winding. The copper bars are short-circuited by copper end rings 28. Terminals would also be provided on the base 21, the number depending on the winding plan adopted.

It `will be understood that while the machine shown in FIG. 1'7 is cylindrical in shape, this is not essential and the invention may equally well be applied to a linear motor. It should also be'mentioned that the use of a cage type secondary winding is not essential and the invention can be put into eiect using other types of secondary windings, for example, wound secondary windgA `description will now be given of the phase-shifting device previously mentioned. Thus referring `to FIG. 1 a section of the co-il assemblies of one phase of the primary and secondary windings is shown. The primary winding comprises the assemblies A and B both of which are the same in conguratio-n but which pass through different slots in the structure. Thus coil assembly A of the primary winding passes through slots 1, 3 and 5 While coil assembly B passes through all the slots 1, 2, 31, 4 and 5. The coil assemblies A1 and B1 of the secondary winding are similarly arranged. The coil assemblies of the primary winding are connected in series to the input terminals IN and the ends connected to one phase of the polyphase supply, and it will be seen that the pole pitch of the field set up by coil assembly A is twice that set up by coil assembly B. The coil assemblies A1 and B1 of the secondary Winding are connected to separate outputs OUT 1 and OUT 2 and the windings are arranged for relative lateral movement. For instance, the structure for the primary winding may be cylindrical in shape and the structure for the secondary winding would then be cylindrical and mounted for rotation within the structure for the primary winding, the primary and secondary windings then corrcsponding to the stator and rotor respectively of an induction regulator. It will be appreciated that the drawing only shows the coils related to one phase whereas normally coils for the other phases will be provided.

It will be appreciated that if the primary winding is energised with the two windings in the relative position shown in FIG. 1, the outputs obtained at OUT 1 and'OUT 2 will be in phase with the input to the primary winding.` However, if one winding is moved relative to the other so that, for instance, the secondary winding takes up a position to the right of that shown in FIG. l, then if this movement introduces a phase difference of 0 between the input IN and the output OUT 1, the phase difference between the input IN and the output OUT 2 will be 20. Thus the phase diiference between the input IN and the output OUT 2 increases twice as rapidly as that between the input IN and the output OUT 1.

It will be understood then for n equal to 4, S, 16 and so on, the number of poles generated by the coil assembly B for each pole generated by the coil assembly A must increase in the same ratio as n, and the arrangement for the case when 11:4 is shown in FIG. 2.

`It will be appreciated that there will be no interaction between the magnetic fields set up by coil assemblies A and B of the primary winding or between the induced fields set up by coil assemblies A1 and B1 because the electromotive forces induced in alternate coils in the assemblies B and B1 are equal and opposite. Similarly there will be no interaction between the field set up by coil assembly A and the induced eld set up by coil assembly B1 or between the iield set up by coil assembly B and the induced field set up by coil assembly A1.

In the case where n is an odd integer, additional acaaaas measures, according to the invention, have to be taken.

For instance, when 11:3 the coil assembly B will comprise three coils for each coil of assembly A but the centre coil .of assembly B will have a different number of turns from that of the outer coils. Similarly for n=5, the assembly B will consist of five coils for each coil of assembly A and again the number of turns in the coils will be different. Other values of n, for 4instance 6, can also be obtained by adopting a similar procedure.

The form of the phase-shifting device, according to the invention, is diagrammatically indicated in FIG. 3. Referring to the drawing, the primary takes the form of a stator i@ while the secondary is in the form of a rotor 11. The stator is mounted on a suitable base 12 and the rotor is provided with a shaft 13 mounted in suitable bearings 14 fixed to the base. One end of the shaft is provided ,with a handwheel 15 for adjusting the relative position of the secondary with respect to the primary. Terminals 16 provide the input to the primary winding from one phase of a three phase supply while terminals 17 provide the secondary output OUT 2 and terminals 18, the output OUT l. lt will be appreciated that the showing of the windings is diagrammatic only and only one phase is represented.

The phase-shifting device according to the invention has particularuse in connection with variable speed induction motors. In United States application 582,820, abandoned in favor of application Ser, No. 851,773, filed November 9, 1959, now Patent No. 2,978,773, a variable speed induction motor is described in which the variation in speed is obtained by electrically varying the direction of movement of the moving magnetic field generated by the stator with respect to the direction of movement of the rotor. The direction of movement of the magnetic field is varied by feeding currents of varying phase to the stator, the variation in phase being effected by `the use of two phase-shifting arrangements of known type. The phase-shifting device of the present invention may be employed to extend the speed range of such a motor without impairing its efciency.

Reverting to the winding plans of the induction machine shown lin FIGS. to 14, it will be seen that within the effective portion of the primary winding, the total number of conductors in the slots is the same for all slots and in the embodiments shown the 4total is 6. It will, however, be understood that the number of conductors need not be 6 as will be seen from the practical embodiment of FIGS. and 16.

We claim:

1. A polyphase induction machine comprising a first slotted structure, a primary winding accommodated in the slots of said first slotted structure, a source of polyphase current, a phase-shifting arrangement fed from said source of polyphase current, a second slotted structure movable with respect to said first slotted structure, a

secondary winding accommodated in the slots of said second slotted structure and electromagnetically coupled to said primary winding, said primary winding consisting of at least first and second sets of coils, said first set of coils being fed from said polyphase source of supply and said second set of coils being fed from said phase shifting arrangement, said first and second coils overlapping so that the magnetomotive force in at least some of thepslots of said first slotted structure is generated by the addition of magnetomotive force caused by current ow in the conductors of coils of both sets, each set of coils being so wound in the slots of said first slotted structure that the magnitude of the current fiow in the conductors of a slot carrying coils of the same phase is different for different slots while the current fed to the sets-of coils in such that the phase difference between the current flow in the conductors of coils of two sets in each slot carrying conductors of two sets of coils is the same for all slots, and means for adjusting the amount of phase shift introduced by said phase-shifting arrangeture is derived entirely from the mains while the currentV in the other end slot of said first slotted structure is derived entirely from said phase-shifting arrangement, the currents in the intermediate slots being derived from the mains and the phase-shifting arrangement in different proportions for different slots.

3. A polyphase induction machine comprising a first slotted structure, a primary winding accommodated in the slots of said first slotted structure, a source of polyphase current, first and second phase-shifting arrangements Y fed from said source of polyphase current for introducing equal and opposite phase shifts in the current fed thereto from said source, a second slotted structure movable with respect to said first slotted structure, a secondary wind-V ing accommodated Ain the slots of said second slotted structure and electromagnetically coupled to said primary winding, said primary winding consisting of a plural-V ity of sets of coils, a first set of said coils being fed from said source of polyphase current while a second and a -third set of said coils are fed from said first and second phase shifting arrangements respectively, said second set of coils overlapping one end of said first set of coils and said third set of coils overlapping the other end of said second set of coils whereby the magnetomotive force in at least some of the slots of said first slotted structure is generated by the addition of the magnetomotive forces caused by current flow in the conductors of coils of two of said sets of coils, each set of coils being so Wound in the slots of said first slotted structure that the magnitude of the current flow in the conductors of a slot carrying coils of the same phase is different for different slots while the current fed -to the sets of coils is such that the phase dierence between the current flow in the conductors of two sets in each slot carrying con-- ductors of two sets of coils is Vthe same for all slots and means for simultaneously adjusting the amount of phase shift introduced by said first and second phase-shifting arrangements into the currents fed to the coils of said second and third sets to enable the speed of movement of said second slotted structure to be varied.

4. A polyphase induction machine as claimed in claim n wherein the current in the central slot of said first Y slotted structure is derived from the mains supply only rangements fed from said source of polyphase current,

the phase shift introduced by said first and second phaseshifting arrangements being equal and opposite while that introduced by said third and fourth phase-shifting arrangements is also equal and opposite and an integral l multiple of that introduced by said first and second phaseshifting arrangements respectively, a second Slotted structure movable with respect to said first slotted structure,

' a secondary winding accommodated in the slot-s of said Afourth and fifth sets of coils being fed by current from said first, second, third and fourth phase-shifting arrangements respectively, one end of said second set of coils overlapping one end of said first set of coils, one end of said third'set of coils overlapping the other end of said rst set of coils, the other end of `said Second set of coils overlapping one end of said fourth set of coils and the other end of said third set of coils overlapping one end of said fifth set of coils whereby the magnetomotive force in at least some of the slots of said irst slotted structure is generated by the addition of the magnetomotive forces caused by current ilow in the conductors of coils of two of s'aid sets `of coils, each set of coils being so wound in the slots of said first slotted structure that the magnitude of the current flow in the conductors of a slot carrying coils of the smc phase is `different for different slots while the current fedr to the Sets of coils is such that the phase y difference between the current ow in the conductors of two sets in each slot carrying conductors of two sets of coils is the same for all slots and means for simultane-l ously adjusting the amount of phase shift introduced by said first, second, third land fourth phase-shifting arrangeand said second and fourth phase-shifting arrangements are each combined into a single phase shifting arrangement having two outputs, the phase shift introduced into one output being an integral multiple of the phase shift introduced into the second output.

7. A polyphase induction machine Aas claimed in claim 6 wherein each phase-shifting arrangement comprises a transformer arrangement having for each phase a primary winding formed by two sets of coils fed from one phase of the -polyphase supply, the number of poles generated by the two sets of coils being in the ratio of 1:2 and a secondary winding formed by two sets of coils having the same conguration as those of the primary winding land individually connected to different outputs, means being provided for effecting relative movement lbetween the primary winding and the secondary Winding.

References Cited in the le of this patent UNITED STATES PATENTS 2,421,298 Sunderland May 27, 1947 2,648,807 Bauer Aug. l1, 1953 2,852,733 Sorkin Sept. 16, 1958 2,856,573 Williams Oct. 14, 1958 

